Sample.MVC Changes: Cleanup, Update Packages and switch to EF6

Lots of changes to the Sample.MVC project:

* Update packages across the board, removed unused packages, consolidate instances of the different versions of the same package being used for different projects
* Cleanup unneeded code - remove things like the AccountsController and login logic (which was from the ASP.net template used to create the sample site, but wasn't actually being used)
* Switch the code first in Sample.MVC to use EF6, new initialization